I saw the original X-men with very low expectations. I was pleasantly suprised and it turned out to be a fairly good movie. Not the best, but a good, solid super hero movie. Two was excellent and three was just sad, a shadow of what it could have been.
Four is a place holder movie. Four is the movie that they could have made if they'd had a decent script, descent effects budget, added in another 40-50 minutes of film and decided to have some real guts. It has things that geeks that know the continuity well like I do will pick up on, including the Striker subplot and highly obscure stuff like Emma Frost having diamond skin, but all of these things are not significant parts of the story. The script itself is....bleh. In some ways it is a solid character development, showing the growing rivalry between Logan and his psychotic brother Victor, but none of the characters are really fleshed out (except MAYBE Striker). They set things up for a Deadpool movie, but the things that are cool about Deadpool the character are woefully lacking in the Deadpool of this film. He is kind of smart alek but....still.
Basically, it is obvious to me that this is the Movie Fox made so that they could keep the rights to the x-men. They set things up in such a way that if they truly wanted to make it a trilogy, they could, with a new team/Generation Next aspect of things, but they didn't really set that well up either. So it was neither an homage to geeks (ala Watchmen) nor was it a cult movie (ala Buckaroo Banzai or Evil Dead or Ghost Rider) nor a Summer Blockbuster/Tentpole Movie (ala Iron Man, Spiderman or the like), but sort of a middling attempt to do something between all three on the minimum budget they could justify and not get sued for Marvel for just trying to hold the copyright.
And Hugh Jackman does a darn good job with the material he's given....which isn't good.